At least 200 people have been wounded in a week of bitter fighting in South Sudan's Jonglei state, the top United Nations humanitarian official in the country said Sunday."Some 200 casualties have arrived in Manyabol", a remote village in the troubled eastern state of Jonglei, where militia gunmen from rival ethnic groups have been battling, U.N. humanitarian coordinator for South Sudan Tony Lanzer said in a statement.Manyabol is only one settlement in a vast region affected by the fighting, raising concerns that the number injured or killed elsewhere in the impoverished state could be far higher.No figures were given on any possible deaths, but Lanzer called on leaders "urgently to halt the cycle of violence that is leading to senseless loss of life and suffering amongst civilians."The U.N. were airlifting the most critically injured to Jonglei's state capital Bor for medical treatment, where Doctors Without Borders (MSF - Medecins Sans Frontieres) are supporting the basic hospital."We've seen gunshot wounds and leg fractures," MSF spokesman Martin Searle told AFP, adding that they had received 22 patients so far. "We're expecting more."Tit-for-tat cattle raids and reprisal killings are common in this grossly under-developed state, awash with guns left over from almost two decades of civil war.But the latest upsurge in fighting that began around a week ago is of a different scale and nature.Local government officials have reported columns of hundreds -- if not thousands -- of gunmen in a tribal militia fighting their way towards the heartland of a rival communityLou Nuer gunmen from northern Jonglei are heading south towards Pibor, an area of their rivals, the Murle.South Sudan's rebel-turned-official army has also been fighting in the region to crush a rebellion led by David Yau Yau, who comes from the Murle people, since 2010.U.S. State Department officials said this week they were "deeply disturbed by mounting reports of abuse of civilians, including targeted killings, rape (and) beatings."